Oil sand extraction processes are used to liberate and separate bitumen from oil sand so that the bitumen can be further processed to produce synthetic crude oil. Numerous oil sand extraction processes have been developed and commercialized, many of which involve the use of water as-a processing medium. One such water extraction process is the Clark hot water extraction process (the “Clark Process”), which was one of the first commercially successful oil sand extraction processes.
A water extraction process such as the Clark Process typically requires that mined oil sand be conditioned for extraction by being crushed to a desired lump size and then combined with water and perhaps other agents to form a conditioned slurry of water and crushed oil sand. In the Clark Process, the water used is “hot” (about 95 degrees Celsius) and an amount of sodium hydroxide (caustic) is added to the slurry to adjust the slurry pH upwards, which enhances the liberation and separation of bitumen from the oil sand. Other water extraction processes may have other temperature requirements and may include other conditioning agents which are added to the oil sand slurry.
The process will typically result in the production of a number of product streams, some of which are typically disposed of as waste. For example, in the Clark Process, these streams include a bitumen froth stream comprising bitumen, asphaltenes, fine particulate mineral solids and water, a middlings stream comprising bitumen, asphaltenes, fine particulate mineral solids and water, and a coarse tailings stream consisting primarily of coarse particulate mineral solids and water. The bitumen froth stream and the middlings stream are typically processed further, both to recover and purify bitumen and to render the fine solids more readily disposable and less of an environmental risk. The coarse tailings stream is not typically processed further, since the coarse particulate solids are relatively easy to dispose of and do not typically present a significant environmental risk.
The bitumen froth stream is processed in a froth treatment process to separate water and solids from the bitumen and to encourage the precipitation of asphaltenes out from the bitumen. The processed bitumen froth stream is then sent for further processing to produce synthetic crude oil. The fine solids and precipitated asphaltenes recovered from the bitumen froth stream are typically ultimately disposed of in tailings ponds.
The middlings stream is processed to recover additional bitumen and to recover water from the fine solids and any precipitated asphaltenes. The fine solids and precipitated asphaltenes recovered from the middlings stream are typically ultimately disposed of in tailings ponds.
The coarse solids previously obtained from the coarse tailings stream may be used to form dykes or berms to contain the fine solids. The water which is recovered from the bitumen froth stream and from the middlings stream may be recycled for re-use in various stages of the processes described above in order to recover valuable heat contained in the water, thus reducing the energy requirements of the various processes.
The froth treatment process reduces the fine solids, asphaltene and water content of the bitumen froth. The froth treatment process typically involves the addition of an organic solvent to dilute the bitumen. The solvent is typically either a naphtha (aromatic) solvent or a paraffinic (saturated aliphatic) solvent. The diluted bitumen froth is typically subjected to a multistage separation process to separate a diluted tailings component (including fine solids and precipitated asphaltenes) from a diluted bitumen component. The diluted bitumen component and the diluted tailings component produced by the multistage separation process are each subsequently subjected to a solvent recovery process.
Recovery of the solvent from the diluted bitumen component is required before the bitumen may be delivered to a refining facility for further processing. Recovery of the solvent from the diluted tailings component is also desirable for several reasons, since any solvent remaining in the tailings will be discarded with the tailings in a tailings pond. First, a loss of solvent becomes an unnecessary expenditure of the extraction process. Second, any solvent remaining in the tailings pond becomes an environmental concern, Third, water in a tailings pond may be recycled and any solvent remaining in this water may create explosive conditions when reheated for re-use in the various processes.
The middlings stream is processed for two main reasons. The first reason to process the middlings stream is to recover amounts of bitumen which remain suspended in the middlings stream. This bitumen is recovered both to maximize the recovery of bitumen from the oil sand and to reduce the amount of bitumen contained in the middlings stream. Since the water recovered from the middlings stream may be heated and recycled for re-use, bitumen remaining in the water may foul heat exchangers and cause a need for increased maintenance of plant equipment.
The second reason to process the middlings stream is to recover water from the middlings stream so that the middlings can be more efficiently disposed of in a tailings pond. The middlings stream contains most of the fine solids from the oil sand, which fine solids tend to settle and consolidate very slowly when their water content is high. Complete settlement and consolidation of the fine material suspended in water may take many years. Furthermore, water not recovered from the middlings stream creates a requirement for makeup water which decreases the overall efficiency of the various processes.
Processes and apparatus relating to the treatment of bitumen froth are described in the prior art. These processes and apparatus include those described in Canadian Patent No. 1,027,501 (Simmer), Canadian Patent No. 1,267,860 (Hann), Canadian Patent No. 1,293,465 (Hyndman et al), Canadian Patent No. 2,021,185 (Tipman et al), Canadian Patent No. 2,149,737 (Tipman et al), Canadian Patent Application No. 2,200,899 (Tipman et al), Canadian Patent Application No. 2,232,929 (Power et al), Canadian Patent Application No. 2,350,907 (Duyvestyn et al), U.S. Pat. No. 4,035,282 (Stuchberry et al) and U.S. Pat. No. 6,007,709 (Duyvestyn et al).
Other bitumen extraction and related processes include those described in Canadian Patent Application No. 2,053,016 (Green et al), Canadian Patent No. 2,055,213 (Wallace et al), U.K. Patent Application No. 2,044,796 (Robinson et al), U.S. Pat. No. 4,324,652 (Hack), U.S. Pat. No. 4,425,227 (Smith), U.S. Pat. No. 4,545,892 (Cymbalisty et al), U.S. Pat. No. 4,722,782 (Graham et al) and U.S. Pat. No. 5,143,598 (Graham et al).
Processes and apparatus relating to the preparation of oil sand slurries and conditioning of oil sand slurries include those described in Canadian Patent No. 2,029,795 (Cymerman et al), Canadian Patent Application No. 2,191,517 (Tipinan), Canadian Patent No. 2,195,604 (Maciejewski et al), U.S. Pat. No. 4,120,775 (Murray et al), U.S. Pat. No. 5,039,227 (Leung et al), U.S. Pat. No. 5,264,118 (Cymerman et al), U.S. Pat. No. 5,954,277 (Maciejewski et al), U.S. Pat. No. 6,007,708 (Allcock et al) and U.S. Pat. No. 6,076,753 (Maciejewski et al).
There remains in the art a need for increased efficiency and effectiveness in treating both the bitumen froth stream and the middlings stream which are produced in the processing of oil sand.